Hydraulic device

ABSTRACT

A hydraulic device having a nut part with a threaded hole which has an internal screw thread with a defined nominal diameter and with a defined, uniform pitch, and having a screw part which has an external screw thread with the same nominal diameter as the threaded hole and with a defined, uniform pitch, which is screwed into the threaded hole. (In hydraulic devices, screw parts, in particular nozzle bodies, are generally adhesively bonded in place, in order to prevent them from becoming detached. Adhesive bonding has certain drawbacks, since the screw threads have to be free of grease, and in the case of nozzles there is a risk of blockages, adhesive can enter the hydraulic circuit and also process reliability is not ensured during application.) There is provided a slight difference between the pitch of the internal screw thread of the nut part and the pitch of the external screw thread of the screw part. This slight difference in pitch while the screw part is being screwed in leads to an elastic deformation of a plurality of thread turns, with the result that the screw part is secured so that it cannot become detached.

FIELD AND BACKGROUND OF THE INVENTION

The invention is based on a hydraulic device, e.g. on a hydraulic valveor a hydraulic pump, the hydraulic device having a nut part, e.g. ahousing or a control piston, with a threaded hole which has an internalscrew thread with a defined nominal diameter and with a defined, uniformpitch, and having a screw part, which has an external screw thread withthe same nominal diameter as the threaded hole and with a defined,uniform pitch, which is screwed into the threaded hole.

It is known, for example from the journal “Industrieanzeiger”, Edition83/88, pp. 24 to 25, to secure a screw part in a threaded hole byadhesive bonding. To do this, the threads have to be free of grease,dirt and moisture. In hydraulic devices, in which the screw part is veryoften a nozzle or a closure screw, which generally has to be exchangedor released and refitted from time to time, the measures required inorder to secure the screw part used in an exchange of this type are verylaborious, since it is difficult to keep the threads free of grease orto remove grease and hydraulic oil which have penetrated into the gapbetween the threads while the hydraulic device is operating. A furtherdrawback is that when the screw part is being screwed into the threadedhole adhesive can flow away or be shaved off and passes into thehydraulic circuit in which the hydraulic device is located. Thiscontaminates the hydraulic fluid which is used. Particularly if thescrew part is a nozzle, there is a risk of the nozzle bore becomingblocked by applied adhesive. Overall, securing a screw by adhesivebonding is laborious, not a very reliable process and is also not clean.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of developing a hydraulicdevice having the features described in the introductory-mentionedparagraph such that the screw part is secured in the threaded hole in asimple manner without the use of adhesive.

In a hydraulic device in accordance with the introductory-mentionedparagraph, the desired object is achieved, according to the invention,wherein there is a slight difference between the pitch of the internalscrew thread of the nut part and the pitch of the external screw threadof the screw part. The difference is selected taking account of thethread turns which engage in one another after the screw part has beenscrewed in, in such a way that individual turns are deformed notpermanently but rather elastically. These elastically deformed turnscause the external and internal screw threads to be elastically clampedtogether, so that the screw part is secured by the forces exerted by theelastically deformed turns.

Although it is known, for example, from U.S. Pat. No. 4,266,590,2,870,668 or 1,922,689 to provide the nut part of a threaded connectionwith a different pitch than the screw part, in a hydraulic device thisparticular type of screw connection has not hitherto been employeddespite the considerable inadequacies of the conventionaladhesive-bonding processes.

Advantageous configurations of a hydraulic device according to theinvention can be found herein.

For example, as has already been indicated, securing a screw by usingdifferent pitches of the internal screw thread and the external screwthread is highly advantageous in particular wherein the screw-in part isa nozzle body in which there is a risk of a blockage if adhesive isused.

In accordance with a feature of the invention the difference between thepitch of the nut part and the pitch of the screw-in part is preferablyin the range from 15% to 10% of a mean formed from the two pitches.

Nozzles have hitherto been made primarily from brass, a material inwhich it is relatively easy to bore holes with a very small diameter ofbetween 0.5 and 1.5 mm. However, brass is relatively inelastic.Moreover, especially with the different pitches between the internalscrew and the external screw thread according to the invention used toclamp the screw threads together, particles may be shaved off, pass intothe hydraulic fluid and contaminate the latter. Therefore, in anotherparticularly advantageous configuration of a hydraulic device accordingto the invention, the screw-in part is made of a steel, in particular ofa free-machining steel. This steel has a high elasticity and can also bemachined easily.

Hitherto, screw parts which have a screw shank, which bears the externalscrew thread, and a screw head and have been screwed into the nut partuntil the head part comes to bear against the nut part, have been usedfor hydraulic devices. If, in accordance with the invention, the screwthreads are provided with different pitches, thread turns are quicklyplastically deformed beyond the elasticity limit if the screw part isrotated further beyond the time when contact is made between the screwhead and the nut part. This causes the securing of the screw to be lost.Therefore, according to still another feature of the invention it isprovided that, to limit the screwing-in movement of the screw-in part,one of the two screw threads has a run-out section in which the depth ofthe thread groove decreases continuously. As soon as the mating screwthread engages in the run-out section of the screw thread, the torquerequired to screw in the screw increases greatly without permanentdeformation at least of the thread turns located outside the run-outsection. In order on the one hand not to give the fitter the feelingthat he has to screw in the screw part so far that a screw head bearsagainst the nut part and, on the other hand, in order nevertheless to beable to provide the screw part with a larger screw head, it is provided,according to yet still another feature of the invention the head,starting from the shank, has a diameter which increases over a definedaxial length. According to still another feature this increasepreferably takes place in the form of a truncated cone.

In another particularly preferred configuration, the internal screwthread of the nut part and the external screw thread of the screw-inpart, in particular the external screw thread of a nozzle, are metricscrew threads with a diameter of 4 mm, the pitch of the first thread,preferably the pitch of the internal screw thread, is 0.7 mm, and thepitch of the second screw thread differs by 0.05 mm from the pitch ofthe first screw thread, and the engagement length between the two screwthreads is approximately 4 mm. According to still a further feature ofthe invention it is preferable for the screw-in part to be hardened onits surface and, according to another preferable feature the screw-inpart can be provided with an oxidation-resistant layer which protectsagainst rust.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of a hydraulic device according to theinvention, which is designed as a pilot-control pressure control valve,is illustrated in the drawings. The invention will now be explained inmore detail with reference to the figures in these drawings, in which:

FIG. 1 shows an excerpt from the main stage of the pressure controlvalve according to the invention, in which a nozzle as screw part isscrewed into the housing as nut part,

FIG. 2 shows an enlarged illustration of the region from FIG. 1 in whichthe nozzle is located,

FIG. 3 shows an excerpt from FIG. 2 which has been enlarged stillfurther and clearly illustrates the engagement between the screwthreads, and

FIG. 4 shows an alternative to the design of the run-out section of thescrew thread of the nozzle which can be seen in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the pressure control valve shown, a bore in a cast iron housing 10securely holds a sleeve 11 in which a main cone 12 is guided and onwhich a seat 13 for the main cone is formed. The main cone 12 is loadedtoward the valve seat 12 by a relatively weak compression spring 14which is located in a rear control space 15, which is filled withcontrol oil. The housing (not shown in more detail) of the pilot valve16, only the circuit symbol of which is illustrated, is seated on thehousing 10. Any design details of the pressure control valve which arenot shown further can be found in the applicant's data sheet RD 25802/01.99.

The pressure which is to be controlled is present in an entry passage 17to the housing 10 and at that end side of the main cone 12 which facesthis passage. When the cone lifts off the seat 13, pressurized liquidcan flow from the entry passage 17, through the end-side opening andthrough radial bores in the sleeve 11, into an exit passage 18 of thehousing 10 and, from there, to a tank.

Passages which are part of a control-oil flow path also run in thehousing 10. A control bore 19, which leads radially from the entrypassage 17, into which a control-oil nozzle 20 is screwed and whichmerges eccentrically into a larger transverse bore 22, which is closedoff with respect to the outside by a stopper 21, lies in the inlet tothe pilot valve 16. In turn, a bore 23, which runs parallel to the axisof the sleeve 11, leads from the transverse bore 22 to the entry to thepilot valve 16. The control space 15 is also connected to this entry viaa line 24. A line, in which a bore 25 of the housing 10 running parallelto the sleeve 11 also belongs, leads from the exit of the pilot valveinto the exit 18 of the housing 10.

Therefore, when the pilot valve 16 is closed, the same pressure prevailsabove the control-oil nozzle 20 in the control space 15 behind the maincone 12 as in the entry 17. The spring 14 therefore holds the main cone12 closed. If the pressure in the entry 17 rises to the value set at thepilot valve 16, the latter opens and control oil can flow out of thecontrol space 15 via the pilot valve 16 into the exit 18. The pressurein the entry 17 still rises slightly by the pressure equivalent of thecompression spring 14 and is then held at this value by a correspondingopening cross section between the sleeve 11 and the main cone 12. Acontrol-oil stream, which is determined by the opening cross section ofthe nozzle and the pressure equivalent of the pressure spring 14, whichis in the region of a few bar, flows via the control-oil nozzle 20.

The nozzle 20 is screwed into the bore 19. For this purpose, this boreis provided over a certain distance, from the larger transverse bore 22,with a metric internal screw thread which has a nominal diameter of 4 mmand a pitch of 0.70 mm. In short, the person skilled in the art wouldsay that the internal screw thread is an M4×0.70 thread.

The nozzle or, more specifically, the nozzle body 20 has a screw shank31 and a screw head 32, the diameter of which, starting from the screwshank, initially increases linearly, in the manner of a truncated cone,with an included angle of 30°, and then remains constant over a shortsection. Therefore, at the screw head 32 it is possible to distinguishbetween a frustoconical section 33 and a cylindrical section 34. On thescrew shank, the nozzle body 20 bears an external screw thread 35 which,like the internal screw thread 30, is an M4 thread, the pitch of which,however, is not 0.70 mm, but rather 0.75 mm, i.e. slightly greater thanthe pitch of the internal screw thread 30. As is clearly apparent, thescrew shank and screw head merge into one another without a recessbetween them. Accordingly, the screw thread 35 also does not end in arecess. Rather, at a short distance from the head 32 the thread groovebecomes gradually less deep and ultimately ends completely in the shank31. This is achieved as a result of the fact that, during the cutting ofthe thread, the cutting tool is drawn back in the radial direction as itcontinues to rotate and as the axial movement of the nozzle bodycontinues. FIG. 3 shows how the thread groove 36 has become shallowerclose to the head 32; while the cutting tool is being pulled out, thespeed of axial movement of the nozzle body is the same as during thecutting of the screw thread ahead of the run-out section, so that evenin the run-out section there is the same distance between the threadturns as in the regular part of the screw thread. The thread end is thennot pointed but rather flat in the run-out section, as can be seen at 37from FIG. 3.

It is also possible, during cutting of the screw thread in the run-outsection, to reduce the speed of the axial movement of the nozzle body20. In this case, as can be seen from FIG. 4, the thread end 37 remainspointed, but the axial distance between two thread turns is reduced inthe run-out section.

The result of the difference between the pitch of the internal screwthread 30 and of the external screw thread 35 is that when the nozzlebody 20, which can be referred to as the screw part, is being screwedinto the bore 19, which can be referred to as the threaded hole, thefront thread turn only bears against a location on a turn of theinternal screw thread if a certain pressure is exerted on the nozzlebody 20 while it is being screwed in. Without this pressure, the rearthread turn of the nozzle body 20 which is in engagement with theinternal screw thread 30 bears against a location on the internal screwthread 30. When the nozzle body 20 has been screwed far enough into thebore 19, a further thread turn comes into contact—albeit by means of theopposite flank—with a flank of the internal screw thread 30. This stateis illustrated in FIG. 3. It can be seen that the thread turn of thenozzle body 20 which has been screwed in furthest is in contact with acorresponding turn of the internal screw thread 30 by means of theinwardly facing flank, and the last turn of the nozzle body 20 which isin engagement bears against a corresponding turn of the internal screwthread 30 by means of the outwardly facing flank. If the nozzle body 20is then rotated further, the turns which are in contact with one anotherare elastically deformed, and the nozzle body 20 and the housing 10 areclamped together, during which process further thread turns can comeinto contact with one another. With the thread dimensions and pitcheswhich have been given, this takes place at a thread length ofapproximately 4 mm. As soon as the situation shown in FIG. 3 is inexistence, or just before this time or just after this time, theinternal screw thread 30 passes into the run-out section of the externalscrew thread 35, so that when the nozzle body 20 is rotated further, thetorque required rises considerably and the rotation of the nozzle bodyis deliberately ended before regular thread turns which engage with oneanother are permanently deformed beyond the elasticity limits of thematerials. In the run-out section there is a certain permanentdeformation of the thread turns, which additionally contributes tosecuring the screw part in the threaded hole.

The particular shape of the head 32, the greater diameter of which isrequired in order to enable a conical widening 41, which influences theflow characteristics of the control oil, to adjoin the actual nozzlebore 40 and to allow introduction of the slot 42, does not allow thefitter to feel that he has to screw in the nozzle body 20 all the way toan axial stop and then tighten it with a high torque, which would entailthe risk of permanent deformation to the thread turns.

The nozzle body 20 is made of a free-machining steel which has goodelastic properties yet can nevertheless be machined easily in order inparticular to be able to drill the very small nozzle bore 40. At itssurface, the nozzle body 20 is hardened, in particular bycarbonitriding, so that there is a low risk of particles being shavedoff when the thread turns are being screwed in and possibly passing intothe hydraulic circuit. Moreover, the nozzle body 20 is provided with anoxidation-esistant layer on its surface.

1. A hydraulic valve having a nut part (10) with a threaded hole (19) which has an internal screw thread (30) with a defined nominal diameter and with a defined, uniform pitch, and having a screw part (20) which has an external screw thread (35) with the same nominal diameter as the threaded hole (19) and with a defined, uniform pitch, which is screwed into the threaded hole (19) wherein there is a light difference between the pitch of the internal screw thread (30) of the nut part (10) and the pitch of the external screw thread (35) of the screw part (20), further wherein the screw part (20) defines a fluid flow passage there through wherein the screw part (20) has a shank (31) which bears the external head (32) and a head (32), in which the diameter of the screw part (20) is greater than in the shank (31), and wherein the bead (32) starting from the shank (31), increases in diameter over a defined axial length.
 2. The hydraulic valve as claimed in claim 1, wherein the screw part (20) is a nozzle body.
 3. The hydraulic valve as claimed in claim 1, wherein the difference between the pitch of the nut part (10) and the pitch of the screw part (20) is in the range from 5% to 10% of a mean formed from the two pitches.
 4. The hydraulic valve am claimed in claim 1, wherein the screw part (20) is made of steel.
 5. The hydraulic valve as claimed in claim 1, wherein to limit screwing-in movement of the screw part (20), one of the two screw threads (30, 35) has a run-out section in which depth of its thread groove (36) decreases continuously.
 6. The hydraulic valve as claimed in claim 5, wherein the external screw thread (35) of the strew part (20) has the run-out section.
 7. The hydraulic valve as claimed in claim 1, wherein the diameter increases linearly to form a truncated cone (33), wherein an included angle of the truncated cone (33) is substantially 30 y.
 8. A hydraulic valve having a nut part (10) with a threaded hole (19) which has an internal screw thread (30) with a defined nominal diameter and with a defined, uniform pitch, and having a screw part (20) which has an external screw thread (35) with the same nominal diameter as the threaded hole (19) and with a defined, uniform pitch, which is screwed into the threaded hole (19), wherein there is a slight difference between the pitch of the internal screw thread (30) of the nut part (10) and the pitch of the external screw thread (35) of the screw part (20), further wherein the screw part (20) defines a fluid flow passage there through wherein the internal screw thread (30) of the nut part (10) and the external screw thread (35) of the screw part (20) are metric screw threads with a diameter of 4 mm, wherein the pitch of a first of the screw threads, the pitch of the internal screw thread (30), is 0.7 mm, and the pitch of a second of the screw threads, the pitch of the external screw thread (35), differs by 0.05 mm from the pitch of the first screw thread, and wherein engagement length between the two screw threads (30, 35) which is determined by a shorter (35) of the two screw threads, is approximately 4 mm.
 9. The hydraulic valve as claimed in claim 1, wherein the screw part (20) is hardened on its surface.
 10. The hydraulic valve as claimed in claim 1, wherein the screw part (20) on its surface has an oxidation-resistant layer.
 11. The hydraulic valve am claimed in claim 4, wherein the screw part (20) is made of a free machining steel.
 12. The hydraulic valve as claimed in claim 9, wherein the screw part (20) is hardened on its surface by carbonitriding.
 13. A hydraulic pump having a nut part (10) with a threaded hole (19) which has an internal screw thread (30) with a defined nominal diameter and with a defined, uniform pitch, and having a screw part (20) which has an external screw thread (35) with the same nominal diameter as the threaded hole (19) and with a defined, uniform pitch, which is screwed into the threaded hole (19), wherein there is a slight difference between the pitch of the internal screw thread (30) of the nut part (10) and the pitch of the external screw thread (35) of the screw part (20) wherein the screw part (20) has a shank (31) which bears the external screw thread (35) and a head (32), in which the diameter of the head (32) is greater than in the shank (31), and wherein the head (32) starting from the shank (31), increases in diameter over a defined axial length.
 14. The hydraulic pump as claimed in claim 13, wherein the screw part (20) is a nozzle body.
 15. The hydraulic pump as claimed in claim 13, wherein the difference between the pitch of the nut part (10) and the pitch of the screw part (20) is in the range from 5% to 10% of a mean formed from the two pitches.
 16. The hydraulic pump as claimed in claim 13, wherein the screw part (20) is made of steel.
 17. The hydraulic pump as claimed in claim 13, wherein to limit screwing-in movement of the screw part (20), one of the two screw threads (30, 35) has a run-out section in which depth of its thread groove (36) decreases continuously.
 18. The hydraulic pump as claimed in claim 17, wherein the external screw thread (35) of the screw part (20) ham the run-out section.
 19. The hydraulic pump claimed in claim 13, wherein the diameter increases linearly to form a truncated cone (33), wherein an include angle of the truncated cone (33) is substantially 30 y.
 20. The hydraulic pump as claimed in claim 13, wherein the screw part (20) is hardened on its surface.
 21. The hydraulic pump as claimed in claim 13, wherein the screw part (20) on its surface has an oxidation-resistant layer.
 22. The hydraulic pump as claimed in claim, 16 wherein the screw part (20) is made of a free-machining steel.
 23. The hydraulic pump as claimed in claim 20, wherein the screw part (20) is hardened en its surface by carbonitriding. 